1. Field of the Invention
The present invention relates to an inverter device.
2. Description of Related Art
In an inverter device that includes an inverter via which a motor is driven, the current value of a current flowing on the source side (will hereafter be referred to as an input source current) relative to the smoothing capacitor is obtained either by detecting the input source current with a current sensor or by estimating an input source current based upon the value detected for the electric current flowing on the inverter circuit side relative to the smoothing capacitor, i.e., based upon the detection value obtained for the inverter DC bus current (hereafter will be simply referred to as a DC bus current) without utilizing a current sensor.
Japanese Patent No. 5069882 discloses an invention that enables detection of the input source current (note that the term “bus DC current in the converter circuit” is used to refer to this current in the above identified patent). However, the addition of a current sensor via which the input source current is detected is bound to lead to an increase in production costs as well as an increase in the amount of installation space required.
In order to address the issues discussed above, Japanese Patent No. 3843391, for instance, discloses an invention pertaining to an art whereby an input source current is estimated, instead of detecting the input source current via a current sensor, by detecting the DC bus current and filtering the detection signal indicating the detected DC bus current and the motor is controlled based upon the estimated input source current.
An ample sampling period over which the DC bus current is sampled must be assured in order to enable detection of the DC bus current.
Japanese Laid Open Patent Publication No. H11-004594 describes a method for assuring a sufficient DC bus current sampling period when detecting PWM pulses at an inverter device and a pulse DC bus current flowing into an inverter under conditions in which the signal difference (the pulse width of a line voltage) between the PWM pulses corresponding to at least two phases among the three phases is less than a predetermined time length by increasing the signal difference between the PWM pulses (the pulse width of the line voltage) so as to achieve the required line voltage pulse width (hereafter the method will be simply referred to as a pulse shift method).
However, when the pulse shift method described above is adopted in the invention disclosed in Japanese Patent No. 3843391, a problem arises in that the extent of current ripple in the DC bus current having undergone filter processing increases.